392 
MR. CHRISTIE ON THE MAGNETICAL OBSERVATIONS 
and the observations, independently of their magnitude, strongly corroborates this 
conclusion. In all the results deduced from the observations at stations from Fort 
Alexander to Fort Resolution, in deducing which the variations observed by Sir John 
Franklin in 1825 have necessarily been employed, these differences indicate that the 
pole of convergence is more remote from the place of observation than the pole of 
verticity ; whereas, in those deduced from observations at stations from Fort Resolu- 
tion to Point Beaufort, in deducing which both the dip and variation are derived 
from Captain Back’s observations, these differences indicate precisely the reverse. 
If, however, we are not to suppose considerable errors in the observations of either 
the dip or variation of the needle, this comparison clearly indicates that the theoretical 
magnetic pole of verticity does not coincide with the pole of convergence, even when 
the positions of these points are deduced from observations made at very limited 
distances from them. 
Having compared the results deduced from Captain Back’s very interesting obser- 
vations with some of those derived from theory, I might now proceed to point out 
the actual positions which these observations, variously combined, would assign to 
the northern magnetic pole of convergence, and also those which, according to this 
theory, they would give to the pole of verticity. As, however, I propose investigating 
this subject with reference not only to Captain Back’s but also to other observations 
made in the same regions, I will reserve this branch of the inquiry for another com- 
munication. 
IV. Intensity of the Terrestrial Magnetic Force. 
The observations which were made by Captain Back for the determination of the 
magnetic intensity were of two kinds, viz. by the time of vibration of a needle in the 
plane of the magnetic meridian, and by the times of vibration of three needles sus- 
pended horizontally, according to Hansteen’s method. 
I shall first discuss the observations which were made with the needle vibrated in 
the plane of the magnetic meridian. This needle is that with which the observations 
for the determination of the dip without the reversion of the poles was made, No. II. 
belonging to the dipping instrument, in which instrument its times of vibration were 
determined. The times of vibration were determined with the face of the instrument 
east and with its face west, the face of the needle being towards the face of the instru- 
ment ; and also, where time admitted, similar observations were made with the 
needle reversed on its axis. In some cases two sets of observations were made in 
each position of the needle. The following Table contains the results of the observa- 
tions which were made at various stations, and, in all cases, on the same spot as the 
corresponding observations for the dip, the two sets of observations having been made 
consecutively. 
